Power system with enhanced thermodynamic efficciency and pollution control

ABSTRACT

An elevated pressure power plant ( 100 ) for cleanly and efficiently oxidizing, gasifying or combusting a fuel. The fuel is oxidized or gasified in a reaction chamber ( 210 ) at a pressure range from approximately 700 psia to 2000 psia, or from approximately 850 psia to 1276 psia. Products of combustion from the chamber may be passed to a heat exchanger ( 224 ). A portion of the condensed water may be recycled to the products of combustion upstream of the heat exchanger. Also, before being passed to the reaction chamber, the coolant may be routed through the heat exchanger in a two-step pressure fashion.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a power plant or system, and moreparticularly, to a low-emission, fossil fuel power plant with enhancedthermodynamic efficiency and pollution control.

[0002] In power plants, such as fossil fuel power plants, a fossil fuelis ignited and burned, oxidized or combusted within a reaction orcombustion chamber under controlled conditions to generate heat. Theheat is transferred to a circulating fluid, such as water, which flowsthrough cooling tubes found in or adjacent to the reaction chamber, togenerate steam. The steam is then passed through a steam turbine togenerate electricity. Integrated Gasification Combined Cycle (IGCC)power plants using solid fuels split the fossil fuel combustion processinto multiple stages where the first stage is typically a partialoxidation or gasification step. Subsequent stages combust the producedgas in gas turbines and steam boilers. Thermodynamic efficiency andpollution control have been and remain important considerations in thedesign of fossil fuel power plants. Conservation concerns, increasingfuel prices, and increasingly stringent pollution control standards arejust a few of the factors that are requiring better, cleaner, moreefficient ways of converting fossil fuels to electricity. Power plantsor systems have achieved relatively high levels of efficiency andpollution control, but they are not without problems. For example, aseffluent particulate standards have become increasingly difficult tomeet, power plants have typically required a number of differentprocesses and pieces of equipment to remove particulate matter. Thisadds to the cost and complexity of the system, and these processes andpieces of equipment typically require substantial power input, leadingto substantial parasitic power losses and inefficiencies. Further,although power plants have occasionally used economizers and similarequipment to recover a portion of the sensible heat from the gases inthe products of combustion, power plants have not attempted to recoverthe latent heat of vaporization of such gases because, under operatingconditions of such plants, the condensation temperatures of such gasesare too low to be efficiently recovered. Particularly in a system inwhich a relatively large amount of gaseous water is produced duringcombustion, the failure to recover any significant portion of suchlatent heat of vaporization can lead to significant thermodynamicinefficiencies.

SUMMARY OF THE INVENTION

[0003] It is therefore an object of the present invention to provide anintegrated power plant or system that recovers the latent heat ofvaporization from produced water, scrubs out acid gases, removeschemical pollutants such as mercury and particulates, and condenses andrecovers liquid carbon dioxide as an integral part of an over-allprocess.

[0004] It is a further object of the present invention to provide apower plant or system offering enhanced thermodynamic efficiency.

[0005] It is a further object of the present invention to provide asystem of the above type that provides for enhanced pollution control.

[0006] It is a still further object of the present invention to providea system of the above type that offers increased flexibility.

[0007] It is a still further object of the present invention to providea system of the above type that allows one to recover at least a portionof the latent heat of vaporization of water produced during oxidation orcombustion.

[0008] It is a still further object of the present invention to providea system of the above type that operates at an elevated pressure makingit thermodynamically practical to recover at least a portion of thelatent heat of vaporization of water produced during oxidation orcombustion.

[0009] It is a still further object of the present invention to providea system of the above type that takes advantage of the useful propertiesof carbon dioxide.

[0010] It is a still further object of the present invention to providea system of the above type that uses recycled, recovered water producedduring oxidation or combustion to provide for reduced equipment costsand reduced equipment wear.

[0011] It is a still further object of the present invention to providea system of the above type that uses a two-stage pressure step-up of thecoolant to reduce heat exchanger equipment costs and reduce heatexchanger wear.

[0012] It is a still further object of the present invention to providea system of the above type that provides for the efficient recovery ofcarbon dioxide for later use or sale.

[0013] It is a still further object of the present invention to providea system of the above type that provides for improved removal ofparticulate matter from products of oxidation or combustion.

[0014] It is a still further object of the present invention to providea system of the above type that provides for the efficient partialoxidation or gasification of solid and liquid fossil fuels.

[0015] Toward the fulfillment of these and other objects and advantages,an elevated pressure power plant or system is disclosed that providesfor cleanly and efficiently oxidizing or combusting a fuel, such as afossil fuel, as follows. The fuel and an oxidant are passed to areaction chamber, and the fuel is oxidized in the chamber at a pressurethat is preferably substantially within a range of from approximately700 psia to approximately 2000 psia and that is more preferablysubstantially within a range of from approximately 850 psia toapproximately 1276 psia. A coolant is passed to the reaction chamber ina heat exchange relationship with the fuel and oxidant. The pressure ofthe reaction chamber is selected so that it is greater than or equal toa liquid-vapor equilibrium pressure of carbon dioxide at the temperatureat which the power plant can reject heat to the environment. Products ofcombustion from the chamber may be passed to a heat exchanger, and watermay be condensed from the products of combustion in the heat exchangerat a pressure that is preferably substantially within a range of fromapproximately 700 psia to approximately 2000 psia and that is morepreferably substantially within a range of from approximately 850 psiato approximately 1276 psia. A portion of the condensed water may berecycled to the products of combustion upstream of the heat exchanger.Also, before being passed to the reaction chamber, the coolant may berouted through the heat exchanger in a two-step pressure fashion so thatthe coolant passes to the heat exchanger at a pressure substantiallywithin a range of from approximately 300 psia to approximately 600 psiaand passes to the reaction chamber at a pressure substantially within arange of from approximately 2000 psia to approximately 5000 psia.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above brief description, as well as further objects, featuresand advantages of the present invention will be more fully appreciatedby reference to the following detailed description of the presentlypreferred but nonetheless illustrative embodiments in accordance withthe present invention when taken in conjunction with the accompanyingdrawings, wherein:

[0017]FIG. 1 is a schematic representation of a power systemincorporating the present invention for fossil-fuels containing minimalor no ash or ash forming materials;

[0018]FIG. 2 is a table showing a preferred, hypothetical set ofoperating conditions for the system depicted in FIG. 1;

[0019]FIG. 3 is a table showing a preferred, hypothetical mass flow ofthe system depicted in FIG. 1;

[0020]FIGS. 4A and 4B are tables showing a preferred, hypotheticalenergy flow of the system depicted in FIG. 1;

[0021]FIG. 5 is a schematic representation of an alternate embodiment ofa power system incorporating the present invention for fuels containingash or ash forming materials;

[0022]FIG. 6 is a table showing a preferred, hypothetical set ofoperating conditions for the system depicted in FIG. 5;

[0023]FIG. 7 is a table showing a preferred, hypothetical mass flow ofthe system depicted in FIG. 5;

[0024]FIG. 8 is a table showing a preferred, hypothetical energy flow ofthe system depicted in FIG. 5;

[0025]FIG. 9 is a schematic representation of an alternate embodiment ofa power system incorporating the present invention; and

[0026]FIG. 10 is a schematic representation of a portion of an alternateembodiment of a power system incorporating the present invention,providing for the use of liquid carbon dioxide to generate energy for anair separation plant.

[0027]FIG. 11 is a schematic representation of a portion of an alternateembodiment of a power system incorporating the present invention,providing for the gasification of solid or liquid fuels to produce aclean synthesis gas which may be used to generate energy in a standardRankine cycle or combined cycle power plant.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] Referring to FIG. 1, the reference numeral 100 refers in generalto an integrated power system of the present invention that integratesthe combustion of fossil fuels and the efficient production ofelectricity with the recovery of liquid carbon dioxide and theelimination of acid gas and particulate emissions. Referring to FIGS. 1and 2, liquid oxygen from tank 202 is pumped to system pressure by pump204. For the system depicted in FIG. 1, the system pressure ispreferably within a range of from approximately 700 psia toapproximately 2000 psia and is more preferably substantially within arange of from approximately 850 psia to approximately 1276 psia. Thispressure range allows one to use standard equipment designs andencompasses the critical pressure of carbon dioxide (1,071 psi or 7.382MPascal). In the later stages of the system, when water and carbondioxide are sequentially condensed, this elevated system pressure rangeallows carbon dioxide condensation at the highest possible temperatureand water condensation at a useful temperature while optimizing systempressure and minimizing overall capital cost. A useful temperature forproduced water condensation is a temperature high enough that standardheat exchangers can readily transfer the heat of vaporization of theproduced water to the coolant.

[0029] The system-pressure liquid oxygen stream 101 passes through heatexchanger 206 where the oxygen is vaporized and raised to near ambienttemperatures. The refrigeration capacity from vaporizing the oxygen isrecovered and recirculated to the oxygen plant. The gaseous oxygen instream 102 is further heated in heat exchanger 208 and then mixed withgaseous carbon dioxide from stream 106. This mixture of oxygen andcarbon dioxide in stream 107 is used as the oxidant in the high-pressurereaction or combustion chamber 210. Mixing the carbon dioxide with theoxygen upstream of the reaction chamber offers a number of advantages.For example, it helps control combustion temperatures by reducing thepeak concentrations of oxygen in the reaction chamber. Although theoxidant is described above as being a mixture of oxygen and carbondioxide, it is understood that a wide variety of oxidants may be used.For example, the oxidant may consist of air or preferably air enrichedin oxygen, mixtures of oxygen in nitrogen, carbon dioxide or other inertgases or most preferably oxygen from an air separation facilitycontaining greater than 85 volume percent oxygen by composition.

[0030] Fuel, such as natural gas from a transmission pipeline 108 iscompressed to system pressure at natural gas compressor 212 and sent viastream 109 to heat exchanger 214 where it is pre-heated. The pre-heatedgas combines with the oxidant in the high-pressure reaction chamber togenerate heat. The heat in the reaction chamber is transferred to acoolant, such as water, in stream 144 that vaporizes into steam bystream 145.

[0031] The coolant, such as boiler feed water and steam, circulatesthrough streams 139 through 148. Water is stored at or near ambienttemperature and essentially atmospheric pressure in boiler-feed-watertank 216. Ambient temperature in this case being the lowest temperatureat which the power plant can routinely reject heat to the environment.Water passes from the boiler water tank 216 to pump 218 at ambienttemperature and pressure via stream 139. This stream condition is set atambient temperature in order to provide the greatest driving forcethrough the steam turbine and thereby generate the most power from thisprocess. Pump 218 pressurizes the water to an intermediate pressure thatis preferably substantially within a range of from approximately 300psia to approximately 600 psia and that is more preferably approximately600 psia. The use of the intermediate pressure as part of a two-steppressure increase for the coolant provides a number of advantages. Forexample, the use of the intermediate pressure allows the 1276 psiastream 113 to enter heat exchanger 224 on the tube side and the 300 to600 psia stream 142 to enter heat exchanger 224 on the shell side. Theshell side pressure of heat exchanger 224 at the intermediate pressureof approximately 300-600 psia is much lower than the typicalhigh-pressure steam pressure of 3500 psia. This simplifies the design ofheat exchanger 224 and adds to the durability of the system. It isunderstood that the boiler feed water feed in stream 142 may be passedto the heat exchanger 224 at a wide range of pressures. The pressure ispreferably selected so that it is greater than the saturated waterpressure at the heat exchanger 224 exit temperature.

[0032] Pump 218 passes the water at ambient temperature and theintermediate pressure to economizer 220 via stream 140. From theeconomizer, the pre-heated water passes via stream 141 to heat exchanger222 and via stream 142 to heat exchanger 224. The pre-heated boiler feedwater at the intermediate pressure passes from heat exchanger 224 topump 226 in a liquid state via stream 143. Pump 226 raises the pressureof the pre-heated boiler feed water to a pressure that is preferablysubstantially within a range of from approximately 2000 psia toapproximately 5000 psia and that is more preferably approximately 3500psia. The boiler feed water passes via stream 144 through the reactionchamber in a heat exchange relationship with the combusting fuel so thatthe combusting fuel gives up its heat of combustion to the water andsteam in the boiler tubes. In the preferred embodiment, sufficient heattransfer surface is available so that the products of combustion exitthe reaction chamber via stream 111 at approximately 900° K or 1,160° F.The boiler feed water is converted to steam and passes via stream 145 toa steam turbine 228 for generating electricity before passing via stream146 to economizer 220 and via stream 147 to condenser 230. Condensedwater passes via stream 148 to the boiler water tank 216 for furthercirculation through streams 139-148.

[0033] The products of combustion or oxidation exit the reaction chamber210 via stream 111 and pass through a catalytic reactor 232. Theproducts of combustion contain carbon dioxide, carbon monoxide, excessoxygen, oxides of sulfur, oxides of nitrogen, diluent gases such asnitrogen and inert gases, produced water in the form of steam, and ashparticles when ash forming materials are present. The catalysts inreactor 232 may be selected to achieve specific desired results.Oxidation catalysts can be used to fully oxidize carbon monoxide, oxidesof sulfur and oxides of nitrogen into carbon dioxide, sulfur trioxideand nitrogen dioxide respectively. Selective catalytic reduction, or SCRcatalysts, can be used with ammonia addition to reduce nitrogen oxidesto nitrogen. Different beds of catalysts can be used in combination toachieve the desired effect. Reactants, such as ammonia, are passed tothe catalytic reactor 232 via stream 112. The treated gases in stream113 are mixed with produced water recycle from stream 123 to form stream114 upstream of heat exchanger 224. The recirculation rate of theproduced water stream 123 is selected so that a portion but not all ofthe water will vaporize and reduce the temperature of stream 114, thecombination of recycled produced water and products of combustion, tothe saturation temperature of water at the system pressure.

[0034] The mixture of recycled produced water and exhaust gases pass viastream 114 through the tube side of heat exchanger 224. Heat exchanger224 transfers heat from the products of combustion passing through thetube side of heat exchanger 224 via streams 114 and 115 to the coolantpassing through the shell side of the heat exchanger via streams 142 and143. Since stream 114 is at system pressure, the water saturationtemperature at this pressure is high enough to allow useful heattransfer and recovery of the latent heat of vaporization of the producedwater. The system pressure is selected so that water condenses from theproducts of combustion at a temperature that is preferably aboveapproximately 450° F. and that is more preferably above 500° F.

[0035] In conventional power plants operated at or near atmosphericpressure, the heat of vaporization energy of the water produced in thecombustion process cannot be economically recovered because the watersaturation temperature or vapor—liquid equilibriun saturationtemperature of the water vapor is approximately 200° F.-220° F., whichis too low. For example, the boiler feed water would typically have atemperature of about 80° F. and the amount of energy that the boilerfeed water could absorb is limited to the enthalpy change between 80° F.and about 212° F. if perfect heat exchange were possible. Practically,perfect heat exchange is not economically possible and a significantthermal driving force is needed to achieve useful heat transfer. Thismeans that the amount of exhaust gas water latent heat energy that couldbe practically absorbed by the boiler feed water is significantly lessthan the enthalpy change between 80° F. and about 212° F. At the typicalsystem pressure of conventional systems, water condenses at a lowtemperature and there is simply an insufficient thermal driving forceand an insufficient temperature rise in the coolant fluid for theeconomic recovery of the heat of vaporization of the produced water.

[0036] The subject power system offers other advantages at heatexchanger 224. For example, the use of the produced water recycle viastream 123 reduces the peak temperature experienced by heat exchanger224 while allowing all or substantially all of the useful heat to betransferred at the water saturation temperature. The heat transfercoefficient of condensing water is typically larger than that of flowinggas. This reduces equipment costs and equipment wear. In addition, asthe gaseous water is condensed in heat exchanger 224, acid gases andparticles will nucleate condensate droplet formation to provide ascrubbing action. This aspect is particularly useful in similar systemsusing fuels such as oil or coal because there are typically greaterlevels of acid gases and particulate matter with these fuels.

[0037] In a preferred mode of operation, heat exchanger 224 is designedand operated so that the condensed water in stream 115 is a sub-cooledliquid and so that the carbon dioxide in stream 115 is above the carbondioxide critical temperature. The vast majority of water in stream 115is removed by knockout drum or vessel 234 as condensate via stream 117.The concentration of carbon dioxide in the condensed, produced water instream 117 is approximately 2 mole percent. The gaseous carbon dioxideleaves the knockout drum 234 via stream 116. Stream 116 passes to heatexchanger 214 to preheat the natural gas from stream 109. Gaseous carbondioxide exits heat exchanger 214 via stream 119 and passes to heatexchanger 236 to vaporize diluent carbon dioxide from stream 105.

[0038] The recycled, produced water and the produced water from knockoutdrum 234 are pumped by pump 238 into stream 120, and stream 120 is splitinto streams 118 and 123. The water in stream 118 passes through heatexchangers 222 and 240 and then passes through a pressure relief valve242. The recycled produced water in stream 123 continues on a recyclecircuit to be combined with the products of combustion in stream 113,upstream of heat exchanger 224. Stream 122 may be used to provide pHadjustment and other chemicals as needed. Such additive chemicals may beused to treat condensed acids. Upon reaching the acid dew point, thesulfur trioxide, SO₃, reacts with water to form sulfuric acid whichcondenses into the liquid phase. The NO₂ may be reacted with a suitablereductant such as formic acid or hydroxylamine to form nitrogen gasaccording to the hydrothermal reactions:

4NH₂OH+NO₂>2½N₂+6H₂O

or,

4HCOOH+2NO₂>N₂+4H₂O+4CO₂

[0039] Another potential reaction is the use of oxalic acid andhydroxylamine to convert nitrogen oxides to ammonium nitrate without thesubsequent production of nitrogen monoxide:

HOOCCOOH+2NH₂OH+2NO₂>2NH₄NO₃+2CO₂

[0040] The separation of oxides of sulfur and nitrogen from the bulk gasstream occurs as an intrinsic simultaneous part of the subject systemoperation. The recovery of the heat of vaporization of the producedwater and the condensation of the carbon dioxide create two separatephase change operations which provide ample opportunity and drivingforce for the conversion and separation of oxides of nitrogen andsulfur.

[0041] It is well-known that gaseous particulates 0.1 to 2.5 microns insize will rapidly nucleate condensation of saturated gases. Smallsuspended particulates reduce the degree of super-saturation needed forcondensate nucleation to negligible levels. The subject system has twophase change operations involving the condensation of saturated gases,water and CO₂. Therefore, it is anticipated that all particulates,including the smallest sub-micron particulates, will be scrubbed andrecovered in the condensed phase.

[0042] Heat exchanger 236 continues the cooling process of the carbondioxide in stream 119. Stream 127 passes from heat exchanger 236 toknockout drum 244 where any dissolved water is separated and blown downas a condensate via stream 128. The gaseous carbon dioxide in stream 129passes to heat exchanger 246 where it is substantially condensed andliquefied. The condensing carbon dioxide provides yet another beneficialscrubbing effect to further remove particulate matter. The coolant orcooling water in streams 153 and 154 used in heat exchanger 246 may alsobe used again in condenser 230.

[0043] The critical temperature of carbon dioxide is 88° F. (31° C.).Below that temperature, carbon dioxide can be condensed into a liquid.Power plants and most chemical plants reject heat to a heat sink in thenatural environment. Often these heat sinks are lakes, rivers or oceans.For example, a plant might draw water from a lake, liver or ocean toprovide a cooling fluid for heat exchangers such as 230 and 246. Suchwater may be withdrawn and returned at high rates so that anytemperature rise in the water is small. A heat sink in the naturalenvironment can also be obtained by the evaporation of water with air.In the most preferred embodiment, devices and systems utilizing orcomprising the subject invention will reject heat to a heat sink, suchas the cooling fluid flowing through lines 153 and 154 of FIG. 1, at atemperature below the critical point of carbon dioxide. Said heat sinkwith a temperature below the critical temperature of carbon dioxideallows the direct condensation of pressurized supercritical or gaseouscarbon dioxide to form liquid carbon dioxide.

[0044] The liquefied carbon dioxide in stream 130 may then be passed toa flash cooler 248 where a portion of the stream may be flashed toprovide cooling for the rest of the stream. Non-condensable gases, suchas nitrogen and excess oxygen, are also purged from flash cooler 248 andvented via streams 131 and 135. The produced and recycled liquid carbondioxide passes via stream 132 through heat exchanger 208 and passes viastreams 137 and 138 to transport 250 and storage 252 facilities,respectively. It is understood that it is not necessary to condense allof the carbon dioxide in stream 129. Instead, a portion of the carbondioxide gas may be recycled to mix with the oxygen upstream of thereaction chamber 210. This reduces heat exchanger and heat rejectionduties.

[0045] Referring to FIG. 5, the reference numeral 300 refers to analternate embodiment of the integrated system of the present invention.In this embodiment, the fuel is a solid fossil fuel containing ash orash forming materials such as bituminous coal. With slight modificationto the fuel input equipment, the same embodiment can be used for liquidfuels containing ash or ash forming materials such as heavy oil andcrude oil. Further still, sour gas may be used as a feedstock. Thesystem may burn CO, CS₂, and H₂S for energy and recover it as sulfuricacid or a sulfate salt. In addition, a Claus process could be integratedin the down stream catalyst, reintroducing H₂S and catalyticallyconverting SO_(x) and H₂S into H₂O and molten/gaseous sulfur.

[0046] The solid ash or ash forming material containing fuel such ascoal is sent to a ball mill, or similar device, 402 that pulverizes thesolid fuel. From the ball mill, the solid fuel passes to a hopper pump404 and passes via stream 301, at or near the system pressure, to amixer 406. For the system depicted in FIG. 5, the system pressure ispreferably within a range of from approximately 700 psia toapproximately 2000 psia and is more preferably substantially within arange of from approximately 870 psia to approximately 1276 psia. Thispressure range allows one to use standard equipment designs andencompasses the critical pressure of carbon dioxide (1,071 psi or 7.382MPascal). In the later stages of the present system, when water andcarbon dioxide are sequentially condensed, this system pressure rangeallows carbon dioxide condensation at the highest possible temperature.Water condensation is achieved at a useful temperature while optimizingsystem pressure and minimizing overall capital cost. Although thepresent system is discussed using coal as the fuel, it is understoodthat other fuels, such as fuel oil, may be used with the system. Ofcourse, if the plant is designed to run on fuel oil only, the ball mill402 and hopper pump 404 may be omitted and a high-pressure fuel oil pumpinserted in their place.

[0047] As discussed in more detail below, liquid carbon dioxide is addedto the mixer via stream 304. Water, surfactants, pH modifiers and otherchemicals may also be added in the mixer.

[0048] After mixing, the mixed fuel and carbon dioxide pass via stream302 to pump 408 before passing to the reaction or combustion chamber 410via stream 307. The fuel and carbon dioxide mixture may also be combinedwith an oxidant upstream of the reaction chamber (FIG. 9). In the caseof fuel oil the mixer may or may not be used depending on the propertiesof the fuel oil. There may be an advantage to making an emulsion of fueloil and liquid carbon dioxide prior to feeding the reaction chamber.Water and surfactants could potentially aid in the formation of fuel oilemulsions with low viscosity and adequate stability. The mixer may notbe necessary, particularly for fuel oils, because when the carbondioxide and coal mixture or the carbon dioxide and fuel oil emulsionenters the reaction chamber and flashes, the rapid expansion and phasechange of the carbon dioxide provides strong mechanical shear anddispersion forces to aid in mixing.

[0049] Liquid carbon dioxide is stored in storage tank 412. Liquidcarbon dioxide flows from the storage tank 412 to the pump 414 viastream 303, and pump 414 raises the pressure of the liquid carbondioxide to the system pressure. Downstream from pump 414, the liquidcarbon dioxide passes via streams 304 and 308 into the mixer 406 andheat exchanger 416, respectively. In a preferred embodiment, sufficientcarbon dioxide passes to the mixer via stream 304 to provide asubstantially equal mass of carbon dioxide and coal in the mixer. In apreferred embodiment, the carbon dioxide in stream 308 is initially astream of liquid carbon dioxide. In order to achieve good mixing withthe gaseous oxygen in stream 306, it is preferred to vaporize the carbondioxide in stream 308 prior to mixing it with the oxygen in stream 306.This may be accomplished by passing stream 308 to heat exchanger 416before the carbon dioxide passes via stream 309 to stream 306 for mixingwith the oxygen to form stream 310.

[0050] Liquid oxygen is stored in storage tank 418. The pressurizedoxygen gas may be obtained by pressurizing liquid oxygen and thenheating and vaporizing it to approximately 240° K in a counter-currentheat exchanger (not shown). The cold liquid oxygen may be used to helpcool the process streams in the air separation plant. The pressurizedgaseous oxygen in stream 305 is further heated in a heat exchanger 422that is used to cool the produced carbon dioxide. The pressurized oxygenpasses from heat exchanger 422 via stream 306 and is ready for mixingwith the carbon dioxide in stream 309. The quantity of oxygen in stream306 is determined by the feed rate of fuel and the expected combustionproducts. In the preferred embodiment, the feed rates of fuel and oxygenare controlled to provide a slight excess of oxygen over the exactschoichiometric ratio between the fuel and oxygen. Prior to injectioninto reaction chamber, the oxygen gas in stream 306 is mixed with thecarbon dioxide gas in stream 309 to reduce the peak concentrations ofoxygen in the reaction chamber. In the preferred embodiment, equalmasses of oxygen in stream 306 and carbon dioxide in stream 309 areused.

[0051] In the reaction chamber, the fuel and oxidant streams arecombined in a series of starved-oxidant combustion steps to control peaktemperatures and heat transfer. Even though diluted by large amounts ofcarbon dioxide, the partial pressure of oxygen in the reaction chamberwill be quite high in the vicinity of the inlet nozzles. An igniter (notshown) may consist of an electrically heated refractory block in closeproximity to the fuel and oxidant feed streams or a chemical such astriethyl aluminium that self-ignites upon exposure to oxygen. Ifnitrogen is not present, NO_(x) gases are not produced. If nitrogen ispresent, NO_(x) may be produced. Among other things, products ofcombustion or oxidation include combustion gases, including producedwater in the form of steam, and ash particles. The products ofcombustion exit the reaction chamber via stream 311 and pass to heatexchanger 424, where the heat exchanger 424 removes heat from stream 311and transfers it to stream 323 that forms part of the boiler feed waterand steam loop.

[0052] A coolant, such as boiler feed water and steam, circulatesthrough streams 321 through 327. Water is stored at ambient temperatureand pressure in boiler water tank 426. Water passes from the boilerwater tank 426 to pump 428 at ambient temperature and pressure viastream 321. This stream condition is set at ambient temperature in orderto provide the greatest driving force through the steam turbine andthereby generate the most power from this process. Pump 428 pressurizesthe water to an intermediate pressure that is preferably substantiallywithin a range of from approximately 300 psia to approximately 600 psiaand that is more preferably approximately 600 psia. The use of theintermediate pressure as part of a two-step pressure increase for thecoolant provides a number of advantages. The use of the intermediatepressure allows the 1276 psia stream 312 to enter the heat exchanger 424on the tube side and the 300 to 600 psia stream 322 to enter the heatexchanger 424 on the shell side. The shell side pressure of the heatexchanger 424 at the intermediate pressure of approximately 300-600 psiais much lower than the typical high-pressure steam pressure of 3,500psia. This simplifies the design of heat exchanger 424 and adds to thedurability of the system.

[0053] The pre-heated boiler feed water at the intermediate pressurepasses from heat exchanger 424 to pump 430 in a liquid state via stream323. Pump 430 raises the pressure of the pre-heated boiler feed water toa pressure that is preferably substantially within a range of fromapproximately 2000 psia to approximately 5000 psia and that is morepreferably approximately 3,500 psia. The boiler feed water passesthrough the reaction chamber 410 in a heat exchange relationship withthe combusting fuel so that the combusting fuel gives up its heat ofcombustion to the water and steam in the boiler tubes. In the preferredembodiment, sufficient heat transfer surface is available so that theproducts of combustion exit the reaction chamber 410 via stream 311 atapproximately 820° K or 1,016° F. The boiler feed water is converted tosteam and passes via stream 325 to a steam turbine 432 for generatingelectricity before passing via stream 326 to condenser 434. Condensedwater passes via stream 327 to the boiler water tank 426 for furthercirculation through streams 321-327.

[0054] Returning to the heat exchanger 424, the portion designed toextract heat from the exhaust gases is designed to operate at a pressurethat is preferably substantially within a range of from approximately700 psia to approximately 2000 psia and that is more preferablysubstantially within a range of from approximately 850 psia toapproximately 1276 psia. The pressure is selected so that watercondenses from the products of combustion at a temperature that ispreferably above approximately 450° F. and that is more preferably above500° F. One important advantage of operating the reaction chamber andheat exchanger at elevated pressure is that the latent heat ofvaporization of the water in the products of combustion can berecovered. At the elevated system pressure, the vapor—liquid equilibriumsaturation temperature of the water vapor is also elevated to a usefultemperature preferably above 450° F. and more preferably above 500° F.).In conventional power plants operated at or near atmospheric pressure,the heat of vaporization energy of the water produced in the combustionprocess cannot be economically recovered because the vapor—liquidequilibrium saturation temperature of said water vapor is approximately200° F.-220° F., which is too low. For example, the boiler feed waterwould typically have a temperature of about 80° F. and the amount ofenergy that the boiler feed water could absorb is limited to theenthalpy change between 80° F. and about 212° F. if perfect heatexchange were possible. Practically, perfect heat exchange is noteconomically possible and a significant thermal driving force is neededto achieve useful heat transfer. This means that the amount of exhaustgas water latent heat energy that could be practically absorbed by theboiler feed water is significantly less than the enthalpy change between80° F. and about 212° F. At the typical system pressure of conventionalsystems, water condenses at a low temperature and there is simply aninsufficient thermal driving force and an insufficient temperature risein the coolant fluid for the economic recovery of the heat ofvaporization of the produced water.

[0055] As mentioned above, it is understood that fuel oil may be usedinstead of coal, in which case, less ash and more water would beproduced and the heat recovered from the latent heat of vaporization ofproduced water would be greater. The intermediate pressure would beadjusted to compensate for this.

[0056] Condensing the water and acid gases within the heat exchanger 424also offers another advantage. During the condensation of water and acidgases, a natural particulate scrubbing action occurs. As the saturatedgases are cooled below the saturation point, droplet formation willnucleate on ash particulates suspended in the gaseous stream. Thiscondensation phase-change scrubbing phenomenon enhances the ash particleseparation and enhances the particulate removal capabilities of thesystem. The heat exchanger 424 is also designed and operated so that theexit temperature of stream 313 is greater than the critical temperatureof carbon dioxide. This provides for enhanced separation of condensedwater and acid gases from the carbon dioxide and improves the quality ofcarbon dioxide produced and captured.

[0057] The cooled products of combustion, including gaseous carbondioxide and condensed water, pass from heat exchanger 424 to knockoutdrum 436 via stream 313. In the knockout drum 436, the liquid water,dissolved acid and ash particulates are separated from the gaseouscarbon dioxide stream. The separated water, acids, and ash flow from theknockout drum 436 to a hydro-cyclone 438 via stream 314 where the ash isseparated from the water. The ash and a portion of the water flows fromthe hydro-cyclone via stream 316 into a cooler 450. From cooler 450, thecooled water and ash flows in stream 317 joins condensed water streams334. 332 and 335 from knockout-drums 444 and 458 to form stream 318,which flows to pressure let-down devices 452. Separations devices suchas filters or reverse osmosis systems 454, can be used to treat the ashand water effluent stream 318. A portion of the cleaned water fromhydro-cyclone 438 passes via stream 315 to pump 440 and is then pumpedvia stream 320 back into stream 312 upstream of the heat exchanger 424.Additives, such as ammonia, caustic, or hydrated lime may be added tothis recycled water via stream 319 to adjust the pH of the recycle waterstream. The advantage of recycling this water is to immediately coolstream 311. Upon water injection, the temperature in stream 311 woulddrop to or near the water liquid—vapor equilibrium temperature at thesystem pressure (570° K, 566° F.). The sensible heat energy in thecombustion gases exiting the reaction chamber at 1,016° F. would beconverted into latent heat in water vapor at a significantly lowertemperature. In the present system, this temperature is approximately566° F. Designing and building a heat exchanger 424 for a peaktemperature and a shell pressure of approximately 566° F. andapproximately 600 psia is easier than designing one for a peaktemperature of approximately 1,016° F. and approximately 1276 psia. Inaddition to the benefits of temperature reduction, steam vaporcondensation has excellent heat transfer characteristics and theadditional water flow will help ensure ash particles are continuallyflushed through the heat exchanger.

[0058] The gaseous stream 328 exiting knockout vessel 436 may containcarbon dioxide and nitrogen. There will also be oxygen and some NO andSO₂. The NO and SO₂ are oxidized with the residual oxygen in thecatalyst bed, 456, into NO₂ and SO₃. Stream 329 is heat exchanged withstream 308 in heat exchanger 416. As stream 329 is cooled into stream330, additional water will be condensed from the gas phase. The fullyoxidized species, NO₂ and SO₃, are readily water scrubbed and convertedinto recoverable materials. This water and acid is recovered in stream332. The recovered NO₂ and SO₃ are separated into Streams 331 and 332 inthe knock-out drum 458. The cooled carbon dioxide, nitrogen and oxygenenter the condenser 442 via Stream 331.

[0059] Stream 343 may be used to provide pH adjustment and otherchemicals as needed. Such additive chemicals may be used to treatcondensed acids. Upon reaching the dew point, the sulfur trioxide, SO₃,reacts with water to form sulfuric acid which condenses into the liquidphase. The NO₂ may be reacted with a suitable reductant such as formicacid or hydroxylamine to form nitrogen gas according to the hydrothermalreactions:

4NH₂OH+NO₂>2½N₂+6H₂O

or,

4HCOOH+2NO₂>N₂+4H₂O+4CO₂

[0060] Another potential reaction is the use of oxalic acid andhydroxylamine to convert nitrogen oxides to ammonium nitrate without thesubsequent production of nitrogen monoxide:

HOOCCOOH+2NH₂OH+2NO₂>2NH₄NO₃+2CO₂

[0061] The separation of oxides of sulfur and nitrogen from the bulk gasstream occurs as an intrinsic simultaneous part of the subject systemoperation. The recovery of the heat of vaporization of the producedwater and the condensation of the carbon dioxide create two separatephase change operations which provide ample opportunity and drivingforce for the conversion, collection, and separation of oxides ofnitrogen and sulfur.

[0062] In an alternate embodiment depicted in FIG. 9, the water, ash andcondensed acid in stream 512 are simply cooled and removed from thesystem via pressure let-down vessels or other pressure reductiondevices. It is highly likely that the calcium and magnesium oxides inthe coal ash will react with the sulfuric acid in the water to producecalcium and magnesium sulfate. The produced water will be treated andreleased or used as cooling water.

[0063] Returning to the embodiment depicted in FIG. 5, the gaseouscarbon dioxide leaves the knockout drum 458 via stream 331. Stream 331passes to condenser 442 where the carbon dioxide is substantiallycondensed and liquefied. The liquefied carbon dioxide in stream 333 maythen be passed to a flash cooler 444 where a portion of the stream maybe flashed to provide cooling for the rest of the stream. In thepreferred embodiment, approximately 20 percent of the carbon dioxide isflashed. When flashed, the liquid carbon dioxide will cool viaJoule-Thompson expansion. This cooling effect can be used to cool theremainder of the liquid carbon dioxide in stream 336. Non-condensablegases, such as nitrogen, excess oxygen, and argon, are also purged fromflash cooler and vented via stream 337. With the presence of this vent,it is clear to those skilled in the art that it may not be necessary touse pure oxygen. Instead, the system may use 90 to 96% oxygen producedby pressure swing adsorption devices or may use air or oxygen enrichedair. The produced and recycled liquid carbon dioxide passes via stream336 through heat exchanger 422 and passes via stream 338 to pump 446that passes the carbon dioxide via stream 341 and 340 to storage 412 andtransport 448, respectively. It is understood that it is not necessaryto condense all of the carbon dioxide in stream 331. Instead, a portionof the carbon dioxide gas may be recycled to mix with the oxygenupstream of the reaction chamber 410. This reduces heat exchanger andheat rejection duties.

[0064] An optional use for the excess liquid carbon dioxide is depictedin FIG. 10. The excess liquid carbon dioxide may be used to provide themotive energy required to produce liquid oxygen. In this embodiment, theliquid carbon dioxide from storage tank 812 passes via stream 751 topump 814 where it is pumped to a pressure greater than its criticalpressure (approximately 7.382 MPa or 1,071 psia). The high-pressurecarbon dioxide then passes via stream 752 to heat exchanger 816 where itis heated above the critical point with waste heat. Since the criticaltemperature of carbon dioxide is so low (304.19° K or 87.5° F.), wasteheat can be used to convert the pressurized liquid carbon dioxide intogaseous carbon dioxide. This heat may come from various parts of thepower plant or from the heat generated by the air and oxygen compressors817 in the air separation plant. The high-pressure gaseous carbondioxide then passes through a turbine 820 to generate motive energy todrive the compressors 817 in the air separation plant. This can be amulti stage operation with supplemental heating of the carbon dioxidebetween the intermediate stages. The spent carbon dioxide may bereleased to the atmosphere at 822, and the liquid oxygen produced maypass via stream 753 through a balance of air separation plant 824, withvent 825, and a pump 826 to a storage tank 818. This approach makes useof the excellent natural properties of carbon dioxide.

[0065] Load leveling of electric power export is achieved by changingthe amount of electric energy directed to the production of oxygen. In adiurnal cycle, during periods of low electricity demand, a largerportion of the plant output is devoted to producing liquid oxygen.During periods of peak electrical demand, the stored liquid oxygen isused and a smaller portion of the plants electric energy is directed tothe air separation plant.

[0066] Other modifications, changes and substitutions are intended inthe foregoing, and in some instances, some features of the inventionwill be employed without a corresponding use of other features. Forexample, the water recycle via streams such as 120, 123, and 315, neednot be or may be used in connection with other designs. Also, thetwo-stage pressure step-up of the coolant via streams 139-144, 321-324and 521-524 need not be used or may be used in connection with otherdesigns. Further, the location of heat exchangers may vary greatly, andthe various streams may be routed to particular heat exchangers in anynumber of configurations. Additionally, the system may be used with orwithout combining carbon dioxide with the fuel, oxygen, or air upstreamof the reaction chamber or in the reaction chamber. Further still, it isunderstood that the carbon dioxide capture and separation need not beused and that the water capture and separation need not be used.Similarly, the selective catalytic reduction or catalytic oxidation neednot be used. Further still, it is understood that all examples andquantitative values and ranges, such as temperatures and pressures, aregiven by way of illustration and are not intended as limitations as tothe scope of the invention. Accordingly, it is appropriate that theappended claims be construed broadly and in a manner consistent with thescope of the invention.

[0067] Referring to FIG. 11, the reference numeral 900 refers to analternate embodiment of the integrated system of the present invention.In this embodiment, the fuel is a solid fossil fuel containing ash orash forming materials such as bituminous coal. With slight modificationto the fuel input equipment, the same embodiment can be used for liquidfuels containing ash or ash forming materials such as heavy oil andcrude oil. The fuel is partially oxidized or gasified to produce anenergy containing synthesis gas. The production of the synthesis gasuses a sub-stoichiometric amount of oxygen and therefore requires lessoxidant than complete combustion.

[0068] The solid ash or ash forming material containing fuel such ascoal is sent to a ball mill, or similar device, 1002 that pulverizes thesolid fuel. From the ball mill, the solid fuel passes to a hopper pump1004 and passes via stream 901, at or near the system pressure, to amixer 1006. For the system depicted in FIG. 11, the system pressure ispreferably within a range of from approximately 700 psia toapproximately 2000 psia and is more preferably substantially within arange of from approximately 870 psia to approximately 1276 psia. Thispressure range allows one to use standard equipment designs andencompasses the critical pressure of carbon dioxide (1,071 psi or 7.382MPascal). In the later stages of the present system, when water andcarbon dioxide are sequentially condensed, this system pressure rangeallows carbon dioxide condensation at the highest possible temperature.Water condensation is achieved at a useful temperature while optimizingsystem pressure and minimizing overall capital cost. Although thepresent system is discussed using coal as the fuel, it is understoodthat other fuels, such as fuel oil, may be used with the system. Ofcourse, if the plant is designed to run on fuel oil only, the ball mill1002 and hopper pump 1004 may be omitted and a high-pressure fuel oilpump inserted in their place.

[0069] As discussed in more detail below, liquid carbon dioxide is addedto the mixer via stream 904. Water, surfactants, pH modifiers and otherchemicals may also be added in the mixer. After mixing, the mixed fueland carbon dioxide pass via stream 902 to pump 1008 before passing tothe reaction or combustion chamber 1010 via stream 907. The fuel andcarbon dioxide mixture may also be combined with an oxidant upstream ofthe reaction chamber (FIG. 9). In the case of fuel oil the mixer may ormay not be used depending on the properties of the fuel oil. There maybe an advantage to making an emulsion of fuel oil and liquid carbondioxide prior to feeding the reaction chamber. Water and surfactantscould potentially aid in the formation of fuel oil emulsions with lowviscosity and adequate stability. The mixer may not be necessary,particularly for fuel oils, because when the carbon dioxide and coalmixture or the carbon dioxide and fuel oil emulsion enters the reactionchamber and flashes, the rapid expansion and phase change of the carbondioxide provides strong mechanical shear and dispersion forces to aid inmixing.

[0070] Liquid carbon dioxide is stored in storage tank 1012. Liquidcarbon dioxide flows from the storage tank 1012 to the pump 1014 viastream 903, and pump 1014 raises the pressure of the liquid carbondioxide to the system pressure. Downstream from pump 1014, the liquidcarbon dioxide passes via streams 904 and 908 into the mixer 1006 andheat exchanger 1016, respectively. In a preferred embodiment, sufficientcarbon dioxide passes to the mixer via stream 904 to provide asubstantially equal mass of carbon dioxide and coal in the mixer. In apreferred embodiment, the carbon dioxide in stream 908 is initially astream of liquid carbon dioxide. In order to achieve good mixing withthe gaseous oxygen in stream 906, it is preferred to vaporize the carbondioxide in stream 908 prior to mixing it with the oxygen in stream 906.This may be accomplished by passing stream 908 to heat exchanger 1016before the carbon dioxide passes via stream 909 to stream 906 for mixingwith the oxygen to form stream 910.

[0071] Liquid oxygen is stored in storage tank 1018. The pressurizedoxygen gas may be obtained by pressurizing liquid oxygen and thenheating and vaporizing it to approximately 240° K in a counter-currentheat exchanger (not shown). The cold liquid oxygen may be used to helpcool the process streams in the air separation plant. The pressurizedgaseous oxygen in stream 905 is further heated in a heat exchanger 1022that is used to cool the produced carbon dioxide. The pressurized oxygenpasses from heat exchanger 1022 via stream 906 and is ready for mixingwith the carbon dioxide in stream 909. The quantity of oxygen in stream906 is determined by the feed rate of fuel and the expected combustionproducts. In the preferred embodiment, the feed rates of fuel and oxygenare controlled to provide a stoichiometric ratio between the fuel andoxygen required for optimum gasification of the fuel. Prior to injectioninto reaction chamber 1010, the oxygen gas in stream 906 is mixed withthe carbon dioxide gas in stream 909 to reduce the peak concentrationsof oxygen in the reaction chamber. In the preferred embodiment, equalmasses of oxygen in stream 906 and carbon dioxide in stream 909 areused.

[0072] In the reaction chamber 1010, the fuel and oxidant streams arecombined in a series of starved-oxidant combustion steps to control peaktemperatures and heat transfer. Even though diluted by large amounts ofcarbon dioxide, the partial pressure of oxygen in the reaction chamberwill be quite high in the vicinity of the inlet nozzles. An igniter (notshown) may consist of an electrically heated refractory block in closeproximity to the fuel and oxidant feed streams or a chemical such astriethyl aluminium that self-ignites upon exposure to oxygen. Ifnitrogen is not present, NO_(x) gases are not produced. If nitrogen ispresent, NO_(x) may be produced. Among other things, products of partialcombustion or oxidation and water-gas shift reactions include combustiongases such as carbon monoxide, hydrogen, carbon dioxide, methane andproduced water in the form of steam, and ash particles. The products ofpartial combustion or gasification exit the reaction chamber via stream911 and pass to heat exchanger 1024, where the heat exchanger 1024removes heat from stream 911 and transfers it to stream 923 that formspart of the boiler feed water and steam loop.

[0073] A coolant, such as boiler feed water and steam, circulatesthrough streams 921 through 927. Water is stored at ambient temperatureand pressure in boiler water tank 1026. Water passes from the boilerwater tank 1026 to pump 1028 at ambient temperature and pressure viastream 921. This stream condition is set at ambient temperature in orderto provide the greatest driving force through the steam turbine andthereby generate the most power from this process. Pump 1028 pressurizesthe water to an intermediate pressure that is preferably substantiallywithin a range of from approximately 300 psia to approximately 600 psiaand that is more preferably approximately 600 psia. The use of theintermediate pressure as part of a two-step pressure increase for thecoolant provides a number of advantages. The use of the intermediatepressure allows the 1,276 psia stream 912 to enter the heat exchanger1024 on the tube side and the 300 to 600 psia stream 922 to enter theheat exchanger 1024 on the shell side. The shell side pressure of theheat exchanger 1024 at the intermediate pressure of approximately300-600 psia is much lower than the typical high-pressure steam pressureof 3,500 psia. This simplifies the design of heat exchanger 1024 andadds to the durability of the system.

[0074] The pre-heated boiler feed water at the intermediate pressurepasses from heat exchanger 1024 to pump 1030 in a liquid state viastream 923. Pump 1030 raises the pressure of the preheated boiler feedwater to a pressure that is preferably substantially within a range offrom approximately 2,000 psia to approximately 5,000 psia and that ismore preferably approximately 3,500 psia. The boiler feed water passesthrough the reaction chamber 1010 in a heat exchange relationship withthe combusting fuel so that the combusting fuel gives up its heat ofcombustion to the water and steam in the boiler tubes. In the preferredembodiment, sufficient heat transfer surface is available so that theproducts of partial combustion exit the reaction chamber 1010 via stream911 at approximately 820° K or 1,016° F. The boiler feed water isconverted to steam and passes via stream 925 to a steam turbine, boileror combined cycle power plant 1032 for generating electricity beforepassing via stream 926 to condenser 1034. Condensed water passes viastream 927 to the boiler water tank 1026 for further circulation throughstreams 921-927.

[0075] Returning to the heat exchanger 1024, the portion designed toextract heat from the exhaust gases is designed to operate at a pressurethat is preferably substantially within a range of from approximately700 psia to approximately 2,000 psia and that is more preferablysubstantially within a range of from approximately 850 psia toapproximately 1,276 psia. The pressure is selected so that watercondenses from the products of combustion at a temperature that ispreferably above approximately 550° F. and that is more preferably above500° F. One important advantage of operating the reaction chamber andheat exchanger at elevated pressure is that the latent heat ofvaporization of the water in the products of combustion can berecovered. At the elevated system pressure, the vapor—liquid equilibriumsaturation temperature of the water vapor is also elevated to a usefultemperature (preferably above 550° F. and more preferably above 500°F.). In conventional power plants operated at or near atmosphericpressure, the heat of vaporization energy of the water produced in thecombustion process cannot be economically recovered because thevapor—liquid equilibrium saturation temperature of said water vapor isapproximately 200° F.-220° F., which is too low. For example, the boilerfeed water would typically have a temperature of about 80° F. and theamount of energy that the boiler feed water could absorb is limited tothe enthalpy change between 80° F. and about 212° F. if perfect heatexchange were possible. Practically, perfect heat exchange is noteconomically possible and a significant thermal driving force is neededto achieve useful heat transfer. This means that the amount of exhaustgas water latent heat energy that could be practically absorbed by theboiler feed water is significantly less than the enthalpy change between80° F. and about 212° F. At the typical system pressure of conventionalsystems, water condenses at a low temperature and there is simply aninsufficient thermal driving force and an insufficient temperature risein the coolant fluid for the economic recovery of the heat ofvaporization of the produced water.

[0076] As mentioned above, it is understood that fuel oil may be usedinstead of coal, in which case, less ash and more water would beproduced and the heat recovered from the latent heat of vaporization ofproduced water would be greater. The intermediate pressure would beadjusted to compensate for this.

[0077] Condensing the water and acid gases within the heat exchanger1024 also offers another advantage. During the condensation of water andacid gases, a natural particulate scrubbing action occurs. As thesaturated gases are cooled below the saturation point, droplet formationwill nucleate on ash particulates suspended in the gaseous stream. Thiscondensation phase-change scrubbing phenomenon enhances the ash particleseparation and enhances the particulate removal capabilities of thesystem. The heat exchanger 1024 is also designed and operated so thatthe exit temperature of stream 913 is greater than the criticaltemperature of carbon dioxide, ammonia, hydrogen sulfide, carbonylsulfide, carbon disulfide and carbon monoxide. This provides forenhanced separation of condensed water and sulfur containing gases fromthe synthesis gas and improves the quality of synthesis gas and carbondioxide produced and captured.

[0078] The cooled synthesis gas or products of partial combustion,including gaseous carbon dioxide, hydrogen, ammonia, carbon monoxide,methane, hydrogen sulfide, carbonyl sulfide, carbon disulfide andcondensed water, pass from heat exchanger 1024 to knockout drum 1036 viastream 913. In the knockout drum 1036, the liquid water, ashparticulates and some dissolved gases are separated from the synthesisgas stream. The separated water, acids, and ash flow from the knockoutdrum 1036 to a hydro-cyclone 1038 via stream 914 where the ash isseparated from the water. The ash and a portion of the water flows fromthe hydrocyclone via stream 916 into a cooler 1050. From there thecooled water and ash flows via streams 917 and 918 to separationsdevices such as a filter 1052, and reverse osmosis system 1053, andknockout drum 1054. Sour gases recovered from the final waste water arereturned for processing to the Claus plant 1055. The other portion ofthe water from the hydrocyclone passes via stream 915 to pump 1040 andis then pumped via stream 920 back into stream 911 upstream of the heatexchanger 1024. Additives, such as oxygen, ammonia, caustic, or hydratedlime may be added to this recycled water via stream 919 to adjust the pHof the recycle water stream. The advantage of recycling this water is toimmediately cool stream 911. Upon water injection, the temperature instream 911 would drop to or near the water liquid—vapor equilibriumtemperature at the system pressure (570° K, 566° F.). The sensible heatenergy in the combustion gases exiting the reaction chamber at 1,016° F.would be converted into latent heat in water vapor at a significantlylower temperature. In the present system, this temperature isapproximately 566° F. Designing and building a heat exchanger 1024 for apeak temperature and a shell pressure of approximately 566° F. andapproximately 600 psia is easier than designing one for a peaktemperature of approximately 1,016° F. and approximately 1,276 psia. Inaddition to the benefits of temperature reduction, steam vaporcondensation has excellent heat transfer characteristics and theadditional water flow will help ensure ash particles are continuallyflushed through the heat exchanger.

[0079] The gaseous stream 928 exiting knockout vessel 1036 may containsynthesis gas, carbon dioxide and nitrogen. The synthesis gas maycontain hydrogen, methane, NH₃, NO, H₂S, COS, CS₂ and potentially SO₂.The COS and CS₂ are reduced by reaction with hydrogen in the catalystbed, 1056, into CH₄, H₂O and H₂S. A catalyst bed could also be used toachieve a water-gas shift reaction to convert carbon monoxide and waterinto carbon dioxide and hydrogen. Stream 929 is heat exchanged withstream 908 in heat exchanger 1016. Stream 943 may be used to provide pHadjustment and other chemicals as needed. Such additive chemicals may beused to treat condensed acids and sulfur containing gases. As stream 929is cooled into stream 930, additional water will be condensed from thegas phase. At temperatures below 100° F. and pressures above 600 psia,H₂S, COS, and CS₂ can be condensed into liquids. A portion of the H₂S isreadily water scrubbed and converted into recoverable materials. Thiswater and dissolved and condensed acid gas stream is recovered in stream932. The condensed and recovered NH₃, H₂S, COS, and CS₂ are separatedinto Streams 931 and 932 in the knockout drum 1058. The cooled carbondioxide, carbon monoxide, methane nitrogen and hydrogen enter thecondenser 1042 via Stream 931.

[0080] The separation of sulfur containing gases from the bulk gasstream occurs as an intrinsic, simultaneous part of the systemoperation. The recovery of the heat of vaporization of the producedwater and the condensation of the carbon dioxide create two separatephase change operations that provide ample opportunity and driving forcefor the conversion, collection, and separation of oxides of nitrogen andsulfur containing gases.

[0081] In the embodiment depicted in FIG. 11, the synthesis gas leavesthe knockout drum 1058 via stream 931. Stream 931 passes to condenser1042 where the carbon dioxide and hydrogen sulfide is substantiallycondensed and liquefied. The liquefied carbon dioxide and hydrogensulfide in stream 933 may then be passed to a knockout drum 1044 wherethe liquid carbon dioxide and hydrogen sulfide is separated from thesynthesis gas and sent via stream 934 to a Claus plant 1055 forconversion to elemental sulfur. In the case where additional cooling ofthe synthesis gas stream 935 was available by heat exchange with oxygenstream 905 in heat exchanger 1022, additional carbon dioxide may becondensed and removed via stream 938 in knockout vessel 1045.Non-condensable synthesis gases, such as nitrogen, carbon monoxide,methane nitrogen, hydrogen and argon, are collected from the knockoutdrum 1045 and directed to the combined cycle power plant 1032 via stream937. The use of the synthesis gas in a combined cycle power plantcomprising a gas turbine and a boiler and steam turbine is the preferredembodiment. Alternately, the synthesis gas could be used directly in asteam boiler. This synthesis gas fired steam boiler could be coupled toor independent of the hot water or steam flow in stream 925. Since thesynthesis gas can be a mixture of combustible gases and non-combustiblegases, it is clear to those skilled in the art that it may not benecessary to use pure oxygen in the initial gasification or partialcombustion step. Instead, the system may use 90 to 96% oxygen producedby pressure swing adsorption devices or may use air or oxygen enrichedair. The produced and recycled liquid carbon dioxide passes via stream935 through heat exchanger 1022, passes via stream 936 through knockoutdrum 1045, and passes via stream 938 to pump 1046 that passes the carbondioxide via stream 941 and 940 to storage 1012 and transport 1048,respectively. It is understood that it is not necessary to condense allof the carbon dioxide in stream 931. Instead, a portion of the carbondioxide gas may be recycled to mix with the oxygen upstream of thereaction chamber 1010. This reduces heat exchanger and heat rejectionduties.

What is claimed is:
 1. A method of operating a power plant, comprising:passing a fuel to a reaction chamber; passing an oxidant to saidreaction chamber; oxidizing said fuel in said reaction chamber at afirst pressure substantially within a range of from approximately 700psia to approximately 2000 psia; and passing a coolant to said reactionchamber in a heat exchange relationship with fuel and oxidant.
 2. Themethod of claim 1, wherein said fuel is a fossil fuel.
 3. The method ofclaim 1, wherein said first pressure is substantially within a range offrom approximately 850 psia to approximately 1276 psia.
 4. The method ofclaim 1, wherein said oxidant comprises oxygen and carbon dioxide. 5.The method of claim 1, wherein said oxidant comprises air, oxygen andcarbon dioxide.
 6. The method of claim 1, wherein oxidizing said fuelcreates products of oxidation, and further comprising: passing saidproducts of oxidation from said reaction chamber to a heat exchanger;and condensing water from said products of oxidation within said heatexchanger at a second pressure substantially within a range of fromapproximately 700 psia to approximately 2000 psia.
 7. The method ofclaim 6, further comprising: separating at least a portion of saidcondensed water from said products of oxidation; and recycling at leasta portion of said separated, condensed water to said products ofoxidation upstream of said heat exchanger.
 8. The method of claim 6,further comprising: passing said coolant from a first pump to said heatexchanger at a first pressure substantially within a range of fromapproximately 300 psia to approximately 600 psia; passing said coolantfrom said heat exchanger to a second pump; and passing said coolant fromsaid second pump to said reaction chamber at a second pressuresubstantially within a range of from approximately 2000 psia toapproximately 5000 psia.
 9. A method of combusting fossil fuel,comprising: passing a fossil fuel into a combustion chamber; passing anoxidant into said combustion chamber; combusting said fossil fuel withinsaid combustion chamber at a first pressure; and passing a coolanthaving an entry temperature to said combustion chamber in a heatexchange relationship with said combusting fossil fuel; said firstpressure being equal to or greater than a liquid-vapor equilibriumpressure of carbon dioxide at said entry temperature of said coolant.10. The method of claim 9 wherein said oxidant comprises oxygen andcarbon dioxide.
 11. The method of claim 10 wherein said first pressureis substantially within a range of from approximately 700 psia toapproximately 2000 psia.
 12. The method of claim 11, further comprising:passing products of combustion from said combustion chamber to a heatexchanger; and condensing water from said products of combustion at asecond pressure within said heat exchanger, said second pressure beingselected so that said water condenses from said products of combustionat a temperature above approximately 450° F.
 13. The method of claim 12wherein said second pressure is selected so that said water condensesfrom said products of combustion at a temperature above approximately500° F.
 14. The method of claim 12 further comprising recycling at leasta portion of said condensed water to said products of combustionupstream of said heat exchanger.
 15. The method of claim 12, furthercomprising: passing said coolant from a first pump to said heatexchanger at a first pressure substantially within a range of fromapproximately 300 psia to approximately 600 psia; passing said coolantfrom said heat exchanger to a second pump; and passing said coolant fromsaid second pump to said combustion chamber at a second pressuresubstantially within a range of from approximately 2000 psia toapproximately 5000 psia.
 16. A method of operating a power plant,comprising: passing a fuel to a reaction chamber; passing an oxidant tosaid reaction chamber; oxidizing said fuel in said reaction chamber tocreate products of oxidation; passing a coolant to said reaction chamberin a heat exchange relationship with said fuel and oxidant; passing saidproducts of oxidation from said reaction chamber to a heat exchanger;and condensing water from said products of oxidation within said heatexchanger at a pressure substantially within a range of fromapproximately 700 psia to approximately 2000 psia.
 17. The method ofclaim 16, further comprising: passing said coolant from a first pump tosaid heat exchanger at a first pressure substantially within a range offrom approximately 300 psia to approximately 600 psia; passing saidcoolant from said heat exchanger to a second pump; and passing saidcoolant from said second pump to said reaction chamber at a secondpressure substantially within a range of from approximately 2000 psia toapproximately 5000 psia.
 18. A method of operating a power plant,comprising: passing a fuel to a reaction chamber; passing an oxidant tosaid reaction chamber; oxidizing said fuel in said reaction chamber tocreate products of oxidation; passing said products of oxidation fromsaid reaction chamber to a heat exchanger; condensing water from saidproducts of oxidation within said heat exchanger; passing a coolant froma first pump to said heat exchanger at a first pressure; passing saidcoolant from said heat exchanger to a second pump; and passing saidcoolant from said second pump to said reaction chamber at a secondpressure higher than said first pressure.
 19. The method of claim 18wherein said first pressure is substantially within a range of fromapproximately 300 psia to approximately 600 psia and said secondpressure is substantially within a range of from approximately 2000 psiato approximately 5000 psia.
 20. The method of claim 18, wherein saidwater is condensed from said products of oxidation within said heatexchanger at a pressure substantially within a range of fromapproximately 700 psia to approximately 2000 psia.
 21. A method ofoperating a power plant, comprising: passing a fossil fuel into acombustion chamber; passing an oxidant into said combustion chamber;combusting said fossil fuel within said combustion chamber at a firstpressure; and passing a coolant having a heat exchange relationship withsaid combusting fossil fuel and a heat sink having a first temperature;said first pressure being equal to or greater than a liquid-vaporequilibrium pressure of carbon dioxide at said first temperature of saidheat sink.
 22. The method of claim 21 wherein said oxidant comprisesoxygen and carbon dioxide.
 23. The method of claim 22 wherein said firstpressure is substantially within a range of from approximately 700 psiato approximately 2000 psia.
 24. The method of claim 23, furthercomprising: passing products of combustion from said combustion chamberto a heat exchanger; and condensing water from said products ofcombustion at a second pressure within said heat exchanger, said secondpressure being selected so that said water condenses from said productsof combustion at a temperature above approximately 450° F.
 25. Themethod of claim 24 wherein said second pressure is selected so that saidwater condenses from said products of combustion at a temperature aboveapproximately 500° F.
 26. The method of claim 24 further comprisingrecycling at least a portion of said condensed water to said products ofcombustion upstream of said heat exchanger.
 27. The method of claim 24,further comprising: passing said coolant from a first pump to said heatexchanger at a first pressure substantially within a range of fromapproximately 300 psia to approximately 600 psia; passing said coolantfrom said heat exchanger to a second pump; and passing said coolant fromsaid second pump to said combustion chamber at a second pressuresubstantially within a range of from approximately 2000 psia toapproximately 5000 psia.
 28. The method of claim 24 wherein saidproducts of combustion comprise products of partial combustion, andfurther comprising: passing said products of partial combustion to aboiler.
 29. The method of claim 24 wherein said products of combustioncomprise products of partial combustion, and further comprising: passingsaid products of partial combustion to a gas turbine.
 30. The method ofclaim 24 wherein said products of combustion comprise products ofpartial combustion, and further comprising: passing said products ofpartial combustion to a combined cycle power plant.
 31. The method ofclaim 24 wherein said products of combustion comprise products ofpartial combustion, and further comprising: passing said products ofpartial combustion to a chemical synthesis plant.